1. Technical Field
The present invention relates to aluminum reflector lighting systems.
2. Background of the Invention
Aluminum sheet material is used commercially in reflector systems for electric lighting fixtures.
Specular aluminum sheet material having higher total reflectance is preferred for commercial reflector systems in the lighting fixtures. By specular is meant relating to, or having the qualities of, a mirror. A higher total reflectance of the aluminum lighting sheet material increases the efficiency of the lighting fixtures and reduces consumption of electricity.
Laminated silver films on reflector lighting products on a steel base are reported to have Total Reflectance (TR) and Distinctness of Image (DI) values of .gtoreq.95%. Although the optical properties of the laminated silver product have customer appeal, silver film reflector products suffer from premature (less than 5 years) delamination and yellowing. Over time, steel suffers from corrosion.
Pankin, U.S. Pat. No. 4,562,517, discloses a method for improving the efficiency of lighting fixtures by providing a reflector coated with a film of silver covered by a polyester or other plastic or a reflector coated with a silver film, e.g., vapor coated, onto the polyester or other plastic. Such reflectors perform adequately for a while, but they are subject to delamination over long periods of time. Moreover, the silver film adds a high cost to the process.
Thin film reflectors incorporating bright dip and anodized (BDA) aluminum sheet provide good TR and DI and further can provide superior abrasion resistance and long life to the layered product. Commercially available BDA reflector material having average total reflectance TR and distinctness of image DI values of 86% and 90%, respectively, with a lifetime warranty of 25 years compete with the laminated silver equivalent, which has TR and DI values greater than 95%. Customer appeal for such BDA thin film reflectors, however, is compromised by cost.
Chemical brightening, also referred to as "bright dip," can provide a bright and specular finish on aluminum sheet material. Bright dip typically can use a phosphoric acid to chemically polish the metal when buffing or electropolishing are not efficient or economical. Bright dipping is a process for increasing the specularity or brightness of aluminum by leveling the microscopic roughness or peaks and valleys on the surface of aluminum sheet and workpieces. The surface of aluminum sheet can be visualized as a series of high and low areas, or peaks and valleys. For a bright dip to smooth this surface, there must be a faster rate of chemical attack and more metal removed at the peaks than in the valleys.
Anodizing is an electrolytic process which produces an oxide coating on aluminum and its alloys for both protective and decorative purposes. Anodizing processes can produce a hard, adherent, protective, and transparent coating of aluminum oxide on a brightened aluminum surface. The protective and clear oxide coating can be produced in an anodizing solution, e.g., containing sulfuric acid. The oxide coating thickness is produced in electrochemical proportion to the electric current employed, or to the time of coating if the electric current remains constant.
Sealing treatments make the porous aluminum oxide coating formed in the anodizing process impermeable, nonadsorptive, and nonstaining. The oxide coating, being porous, decreases the coating resistance to corrosion and increases undesirable staining and coloring. Generally, sealing can be accomplished by treating anodized surfaces in hot water.
Specular aluminum sheet materials produced by bright dip and anodizing processes typically can have a total reflectance of about 87% or more. This higher total reflectance of specular sheet material increases the efficiency of lighting fixtures and reduces consumption of electricity.
However, the higher total reflectance from bright dip and anodizing comes at a cost. Chemical brightening and electrochemical anodizing is costly in the form of process requirements for substantial electrical power, process chemicals, and process manpower together with the high cost associated with proper environmental disposal of the spent chemicals required in the bright dip and anodizing process operations.
Accordingly, a novel process is needed for providing higher total reflectance of aluminum sheet material to increase the efficiency of lighting fixtures and further to reduce consumption of electricity, to provide for enhanced formability of the sheet material without crazing, and to reduce high environmental costs.